Process for crumpling synthetic suede

ABSTRACT

Preparing suede-like leather sheet materials by passing a napped sheet with a fluid through a venturi-nozzle having a predetermined inner area. The sheet has naps of superfine denier fiber at least on one surface, and comprises (a) a non-woven fabric made up to 0.01-0.3 denier superfine staple fibers of breaking strength below 3 grams and an elongation at break of 60180 percent and (b) a polyurethane elastomer obtained by reacting a diol mixture by weight of about 20-40 parts of polycaprolactone diol of a molecular weight of about 1000-3000 and about 60-80 parts of polytetramethyleneetherglycol of a molecular weight of about 1000-3000 with an organic diisocyanate and a diamine chain extender.

United States Patent [191 Okazaki et al.

[ PROCESS FOR CRUMPLING SYNTHETIC SUEDE [75] Inventors: Kaoru Okazaki, Otsu; Kenkichi Yagi, Kyoto; Miyoshi Okamoto, Takatsuki; Koji Watanabe, Otsu; Toyohiko Hikota, Godocho; Masayoshi Kubo, Kusatsu, all of Japan [73] Assignee: Toray Industries, Inc., Tokyo, Japan [22] Filed: Mar. 6, 1973 [21] Appl. No.: 338,565

[52] US. Cl. 8/17; 8/4; 8/151; 8/152; 28/76 [51] Int. Cl D06p 7/00 [58] Field of Search 8/4, 152; 68/D1G. 1, 17

[56] References Cited UNITED STATES PATENTS 2,524,119 10/1950 Van Heek 26/2 2,978,291 4/1961 Fahringer 8/151 Aug. 12, 1975 Primary Examiner-Donald Levy 5 7 ABSTRACT Preparing suede-like leather sheet materials by passing a napped sheet with a fluid through a venturi-nozzle having a predetermined inner area. The sheet has naps of superfine denier fiber at least on one surface, and comprises (a) a non-woven fabric made up to 0.01-0.3 denier superfine staple fibers of breaking strength below 3 grams and an elongation at break of 60-180 percent and (b) a polyurethane elastomer obtained by reacting a diol mixture by weight of about 20-40 parts of polycaprolactone diol of a molecular weight of about 1000-3000 and about 60-80 parts of polytetramethyleneetherglycol of a molecular weight of about 1000-3000 with an organic diisocyanate and a diamine chain extender.

18 Claims, 1 Drawing Figure PROCESS FOR CRUMPLING SYNTHETIC SUEDE Background of the Invention This invention relates to a process for preparing synthetic suede sheet materials.

We have previously disclosed a synthetic suede comprising islands-in-a-sea type fibers and polyurethane elastomer. as described in US. Pat. No. 3.531.368. lndeed. synthetic suedes having naps on the surface were obtained according to such disclosure. The resulting synthetic suedes. when they were dyed. were subject to improvement in respect of hand characteristics. such as flexibility and suppleness and aesthetic characteristics. such as graceful writing effect of finger marks on the surface. and appearance of naps such as fineness. density. etc. We found that such synthetic suede cannot be obtained only by the application of known materials and known producing methods.

According to the present invention it becomes possible to obtain synthetic suede leather having satisfying hand characteristics. a deep tone of colors and graceful aesthetic characteristics which have never been accomplished until now.

An object of this invention, therefore, is to provide a process for producing synthetic suede leathers which possess flexible and supple naps on the surface densely arranged, and which show a graceful writing" effect of finger marks in a manner remarkably like natural suede. Another object is to provide a process for producing synthetic suede leathers which possess a flexible and supple touch and do not cause difficulties in the dyeing process. such as uneven dyeing. cracks on the surface. tear and wear. for example.

DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENTS The objects of this invention are accomplished by passing a napped sheet with a fluid through a venturi-nozzle which has an internal cross-sectional area in the region shown by formulas l and (2) as follows:

and

S 300 (cm wherein S is the cross-sectional area internally of the venturinozzle (cm and A is the cross-sectional area of the napped sheet. said napped sheet having naps of superfine denier fiber at least on one surface and having a thickness of about 0.2-4.0 mm and a width of about 5-200 cm. and comprising (a) a non-woven fabric made up of 001-0. denier superfine staple fibers of a breaking strength below 3 grams and an elongation at break of 60-l 80 percent and (b) a polyurethane elastomer obtained by reacting a diol mixture. by weight. of about -40 parts of polycaprolactone diol ofa molecular weight of about l000-3000 and about 60-80 parts of polytetramcthylene ethcrglycol of a molecular weight of about 1000-3000 with an organic diisocyanate and a diamine chain extender.

It has become clear that not only the specific polyurethane. but also the specific superfine denier fiber and the specific dyeing method are necessary to realize the objects of this invention. We have found that the specific dyeing method of crumpling the sheet by passing it through a narrow venturi-nozzle repeatedly in dyeing liquid at a high temperature of about -l 50C is most effective for dyeing such sheet material. According to our investigation the napped sheet comprising the above-described specific polyurethane and fiber material combines with such specific dyeing method and provides a synthetic suede having good flexibility. graceful naps on its surface and good dyeing properties.

Usual polyesterpolyurethanes cannot resist the effects of the high temperature dyeing process of this invention, so sheets containing such polyurethane tend to develop surface cracks after dyeing and to tear or wear during dyeing according to this invention. Such sheets tend to have an inflexible touch. The sheets comprising polycaprolactonepolyurethane are not an exception.

Polyetherpolyurethane. especially diamine extended polytetramethyleneetherglycol polyurethane is often used as a polyurethane which should be durable to dyeing at high temperature because of its good hydrolysis resistance and heat resistance. Indeed. a napped sheet containing such polytctramethyleneetherglycol polyurethane provides a colored sheet by the dyeing process of this invention. but the resulting dyed sheet tends to show a strong rubber-like repulsive elasticity and an inflexible touch. Further. the aesthetic characteristic of the naps of the sheet is poor. Namely. the dyeing process of this invention is ineffective for softening the napped sheet made from polytetramethyleneetherglycol polyurethane. Thus. in the case of polycaprolactone diol-type polyurethane or polytetramethylenecthcrglycol-type polyurethane. an unsatisfactory sheet is provided by the dyeing method of this invention including crumpling the sheet by passing through a narrow venturi-nozzle at high temperature.

It has become clear from our investigations that a block polyurethane containing both a polycaprolactone diol segment and a polytctramethyleneetherglycol segment in a specific ratio range is necessary for accomplishing the objects of this invention. Only such specific block polyurethane can provide a napped sheet material which may become sufficiently flexible without resulting defects upon dyeing by the dyeing process of this invention.

The softening effect by dyeing according to this invention is not remarkable in a sheet comprising a polytetramethyleneethcrglycol type polyurethane. On the other hand. this effect is remarkable in a sheet comprising the above-described specific block polyurethane of this invention. That is to say. the reduction ratio of the flexibility value. defined later. of a sheet comprising polytetramethyleneetherglycol type polyurethane is ncar zero; on the other hand that of a sheet comprising the specific polycaprolactone-polytetramethyleneetherglycol type block polyurethane is beyond 20 percent; moreover there is no reduction of dyeing resistance as with a sheet comprising polyesterpolyurethane.

In the case of the polytetramethyleneethcrglycol type polyurethane. the rubber-like elasticity of the sheet is not relaxed by the crumpling effect in a hot water bath. i.e. the influence of both chemical and physical effects. and does not provide a graceful synthetic suede which is the object of this invention. On the other hand. in the case of the block-polyurethane of this invention which contains a polyeaprolactone diol segment including ester groups in its main chain. the napped sheet acts properly through the dyeing process of this invention. for example. adhesion between the fiber and the polyurethane decreases due to a erumpling effect in a hot water bath so that the flexibility of the sheet increases and graceful synthetic suedes. which have never been obtained until now. are provided. This is also considered as a reason why the properties of the naps are improved. lt appears that the polyurethane surrounding the root of the nap is softened by the dyeing of this invention and it becomes easy for the nap to move freely so that the writing effect" of naps. appearance of tinger marks and so on. are improved.

Polytetramethyleneetherglycol type polyurethane is almost insoluble in dimethylsulfoxide. but the block polyurethane of this invention is easily soluble in that solvent. This fact shows that there is a remarkable difference between both types of polyurethane. Further. the wet coagulated block polyurethane of this invention takes on a non-microporous structure when observed through a microscope. On the other hand. the wet coagulated polytetramethyleneetherglycol type or polyalkyleneether type polyurethane seems to take on a microporous structure according to the description in U.S. Pat. No. 3.067.483. This is also a major difference between the respectives polyurethanes.

The foregoing explanation suggests that the content of the polycaprolactone diol in the diol mixture plays an important part in the polyurethane of this invention. Practically. an excessively high content of polycaprolactone causes cracks or tears upon dyeing the sheet. Such sheet does not become flexible through dyeing as compared to its flexibility before dyeing. On the other hand. an excessively low content of polycaprolactone does not provide a flexible sheet through the dyeing of this invention. because such polyurethane has almost the same properties as the polytetramethyleneetherglycol type polyurethane. The preferable range of the ratio (by weight) of polycaprolactone diol to polytetramethyleneetherglycol in the diol mixture is 20/80 40/60. more preferably 20/80 35/65.

The diol component of the polyurethane of this invention contains partly polycaprolactone diol. Polycaprolactone diol is a polyester diol. but every polyester diol is not always usable. For example. when polyethyleneadipate diol or polybuthyleneadipate diol is used instead of polycaprolaetone diol. the resulting sheet tends to be inflexible and to develop cracks upon dyeing on its surface, even if other conditions of this invention are satisfied. It seems therefore that stability in the process of production is insufficient in such cases.

As a reason it is considered that the resistance to hot water of the chain-opening type polyester. such as polycaprolactone diol. is better than that of the condensation type polyester, such as polyethyleneadipate diol. Accordingly. we have found that the specific structure of polyurethane is necessary for this inven tion.

The method of producing the polyurethane is described as follows:

The block polyurethane of this invention is prepared by reacting a diol mixture of about 20-40 parts of polycaprolactone diol of a molecular weight of 1000-3000 and about 6080 parts of polytetrame thyleneetherglyco] ofa molecular weight of 1000-3000 with a molar excess of an organic diisocyanate to yield an isocyanatcterminated intermediate called a prepolymer. dissolving said prepolymer in an organic solvent. and further reacting said prepolymer with a diamine chain extending agent.

Organic diisocyanates which are useful for the preparation of the block polyurethanes of this invention include preferably aromatic diisocyanates such as diphenylmethane-4.4'-diisocyanate. tolylene diisocyanate. naphthylene diisocyanate. diphenyl diisocyanate and xylylene diisocyanate. and aliphatic diisocyanates such as hexamethylene diisocyanate and lysine diisocyanate.

Chain extending agents which are usable in this invention are restricted to diamines, especially diamines having primary amino groups. Diamines having at least one secondary amino group. glycols and aminoalcohols are unsuitable because the resulting sheet cannot resist the dyeing conditions of this process. Such primary diamines include hydrazines. aliphatic diamines such as ethylene diamine. propylenediamine, trimethylenediamine. tetramethylene diamine. pentamethylenediamine. hexamethylenediamine and 1.4- diaminopiperazine and aromatic diamines such as phenylenediamine. tolylenediamine, naphthylenediamine and 4.4-diaminodiphenylmethane. Aromatic diamines are preferable in the respect of a heat resistance and a dyeing resistance at high temperature. The most preferable combination of a diisocyanate and a diamine is that of diphenylmethane-4.4-diisocyanate and 4.4-diaminodiphenylmethane.

The solvents which are used in this process are required to dissolve the .diamine chain extended polyurethane. Such solvents include dimethylformamide. diethylformamide. dimethylacetamide. dimethylsulfoxide and hexamethylphosphoramide.

For adjusting the viscosity of polyurethane monofunctional compounds such as di-n-butylamine. diethylamine. di-n-propylamine and aniline may be added during the preparation of the polyurethane.

In the case of the above-described most preferable combination of diisocyanate and diamine. the structure of the polyurethane is shown as follows:

wherein O-G-O is a polycaprolactone diol residue or polytetramethyleneetherglyeol residue and comprises. by weight. about 20-40 percent of polycaprolactone diol residue and about 60-80 percent of polytetramethyleneetherglycol residue, A is a difunctional organic residue shown by the formula p is an integer from 1 to 3 and n is an integer at least 1. That is to say. the polyurethane which contains the repeating structure of several A units is the most preferred polyurethane of this invention. Such structure and content of polycaprolactone diol in the diol component seems to be more the essential factors which give good dyeing resistance and flexibility to the resulting sheet.

In this invention superfine 0.01 0.3 denier staple fiber of an elongation at break of 60-18071 and of a breaking strength of below 3 grams is used as the fiber of the non-woven fabric. A preferred fiber is superfine denier polyester fiber, especially superfine polyethyleneterephtalate fiber. Practically, it is most preferable to use a superfine denier fiber in the form of bundles each comprising at least about five fibers, but the superfine denier fiber is usable also in the form of random web.

Special attention should be paid to the elongation at break of the fiber of this invention, because of its higher elongation value in comparison with known fibers for non-woven fabrics. The elongation at break of the apparel use fiber known until now must be in the region of about -35 percent to prevent a permanent deformation of the product upon wearing, and to give proper resilience to the product. The elongation at break of the fiber is thus greatly restricted, because such practical problems tend to occur when using a fiber of excessively high breaking elongation for apparel use. This invention ovcrthrows such a generally accepted idea. The products of this invention are usable for such purposes, although the breaking elongation of fiber is extremely high.

This invention offers several advantages as follows, by using such high elongation superfine denier fibers. Generally, the degree of intertwining of fibers more greatly influences the properties of a nonwoven fabric than the characteristics of the fiber, and in this case the strength of the non-woven fabric increases by using the superfine denier fiber. In the case of a non-woven fab ric the number of fibers per unit cross-sectional area may be increased more than in the case ofa fabric, and

therefore the amount of deformation caused by a given external force is repressed. Further, the problem of uneven dyeing of the synthetic suede comprising such fiber and polyurethane may be solved.

When the napped sheet comprising the polyurethane and the fiber having a general elongation at break of 30-35 percent is dyed through a process otherwise the process of this invention, the resulting product tends to show uneven dyeing, such as polyurethane being fully colored and fiber being little colored, or polyurethane and fiber being dyed in different colors because of different affinity for the dye, or different rate of exhaus tion of dye between the fiber and the polyurethane. Concretely, the color differs between naps of the sheet made from fiber and the skin of the sheet made from polyurethane. The high elongation superfine denier fiber, however, has similar properties on dyeing to the polyurethane elastomer in this invention, so the resulting sheet never shows uneven dyeing between the naps and the skin. This is explained from the results obtained by FIG. 1.

FIG. 1 shows the relation of the dye adsorption and dye concentration of the bath in the dyeing process of this invention at the following conditions: temperature: 130C, time: 1 hour and dye: Terasil Orange SRL (Color Index No. Dis. Orange Curve 1 shows the relation for the 0.1 denier polyethyleneterephtalate fiber having an elongation at break of 90 percent and a breaking strength of 0.6 grams, which forms fiber bundles. Curve 2 shows the relation for the polyurethane of this invention used in Example 1. Curve 3 shows the relation for the 0.1 denier polyethyleneterephtalate fiber having an elongation at break of 35 percent and a breaking strength of 5.0 grams, which deviates from this invention. Namely the relation for the high elongation superfine denier fiber of this invention (Curve 1) almost coincides with the relation for the polyurethane (Curve 2) in the practical dye concentration (until about 10% o.w.f.). On the other hand the relation for the general elongation fiber (Curve 3) considerably deviates from Curve 1 and Curve 2. When such fiber is applied to this invention practically, the resulting products show the uneven dyeing between naps and skin because of the lower dye adsorption of the fiber and therefore the objects of this invention are not accomplished. It is clear from FIG. 1 that such difference of adsorption between both fibers is remarkable in the region of deep color, which is especially desirable in the leatherlike products.

Preferably the denier of the superfine denier fiber is in the region of 0.01-0.31, more preferably 0.050.2. Excessive decrease in denier causes lowering of the breaking strength of the fiber, which causes poor raising properties of the sheet such as wear and tear of naps, and furthermore causes excessive increase of reflection of light by the surface of the sheet so that the color of the sheet never becomes clear.

Excessive increase in the elongation at break of the superfine denier fiber makes the permanent deformation of the sheet so large because of approaching the undrawn state that the resulting product tends to lose its shape in wearing. Excessive increase in breaking strength of fiber (as beyond 3 grams) brings poor raising properties of the sheet and tends to cause pills on the surface of the sheet. On the other hand excessive decrease in breaking strength brings wear and tear of naps. The preferred inferior limit is about 0.01 g. In the region of the elongation at break and the breaking strength of this invention the strength of the naps is sufficient and the resulting product possesses a graceful napappearance.

The superfine denier fiber of this invention is prepared by means of the general melt-spinning method of a specific method comprising spinning at least two different polymers from a single orifice and dissolving at least one component from the resulting multicomponent fiber, such multi-component fiber known as an islands-in-a-sea type fiber, a polymer blend type fiber that is a filament of an intimate mixture of two mutual incompatible fiberforrning organic polymers, a multi-layer type fiber, a side-by-side type fiber and a core and sheath type fiber. The islands-in-asea type fiber and the polymer blend type fiber are useful, in particular the islands-in-a-sea type fiber is most suitable for this invention in the respect of appearance of naps.

A method of producing such islands-in-a-sea type fiber is described in U.S. Pat. No. 3,531,368. In the present invention it is the most preferred method to use the fiber bundles which are obtained by eliminating the sea component of said islands-in-a-sea fiber. The superfine denier fiber of this invention may be produced through the process described in U.S. Pat. No. 3,531,368, with proper modification or combination of the conditions of fiber manufacture. When a superfine denier fiber of higher breaking elongation is needed, it is possible to decrease the draw ratio at drawing. A super-draw effect of polyethyleneterephtalate is usable. The heat treatment with relaxation is also useful in such case. The control of the breaking strength of the fiber is accomplished by altering the degree of polymerization of the polymer. the fiber denier (increase and de crease of the number of islands in the islands-in-a-sea fiber), the temperature at drawing. etc. As described above. the elongation and the strength of the fiber are changeable independently. so one who is experienced in fiber manufacture can easily prepare the fiber of this invention.

There are various methods for producing the synthetic suede comprising the above-described superfine denier fiber and the block polyurethane. One of the representative methods comprises impregnating the non-woven fabric with the solution of the block polyurethane, said non-woven fabric obtained by the process comprising forming a web from the abovementioned multi-component fibers such as islands-in-a sea type staple fiber. etc. intertwining the web by needle punching or other methods. and dissolving the soluble component of the fiber with a solvent. Then the impregnated sheet is wet-coagulated in water, dried and buffed to obtain a napped sheet. and then dyed by passing repeatedly, together with the fluid. through a venturi-nozzle which has a specific internal cross-sectional area. Another preferred method comprises setting the non-woven fabric with a water-soluble binder such as polyvinylalcohol or carboxymethylcellulose in an aqueous solution. then dissolving the soluble component of the fiber to obtain a sheet made of the superfine denier fiber, impregnating said sheet with a solution of the block polyurethane of this invention, wet-coagulating in water. extracting the water-soluble binder and the solvent in hot water. and then buffing and dyeing in accordance with the described procedure.

A suitable ratio of the impregnated polyurethane weight to fiber weight is in the region of about /100 100/100. Of course. a slicing and pressing process may be added to the procedure to control the thickness of the napped sheet. Further. a finishing buff or a softening treatment may be applied to the dyed sheet which is sufficiently flexible and has a graceful nap appearance. akin to that of high quality natural suedes.

In this invention it is most important to pass the napped sheet repeatedly together with a fluid through a venturi-nozzle possessing a specific cross-sectional area of its hollow portion to impart a crumpling effect to the sheet. The ratio of the cross-sectional area of the hollow portion of the venturi-nozzle to that of the napped sheet strongly influences this crumpling effect. The venturi-nozzle may be selected upon the basis of its caliber, when the cross-sectional shape is circular. But the shape is not always required to be circular and it may be polygonal, elliptical or any other regular or irregular shape, so the cross-sectional area of the hollow part of the venturi-nozzle becomes important. Excessive increase in the ratio of the cross-sectional area of the hollow part of the venturi-nozzle to that of the napped sheet causes an insufficient crumpling effect in the sheet, so that the resulting product becomes inflexible, the appearance of naps is not graceful and the color fastness of the sheet becomes inferior. On the other hand, excessive decrease in the ratio imparts an extremely strong crumpling effect to the sheet, so that the sheet tends to become fatigued and therefore loosening or tearing occurs during dyeing. A preferable cross-sectional area of the hollow part of the venturinozzle is related to the width and thhickness of the sheet, and in this invention the ratio of the crosssectional area of the hollow part of the venturi-nozzle to that of the sheet should be in the range from 2 to 22. and the value of the cross-sectional area of the hollow part of the venturi-nozzle is in the region from 10 to 300 (em When the cross-sectional area of the hollow part of the venturi-nozzle exceeds 300 cm disadvantages occur in manufacturing the nozzle and installing the nozzle in the dyeing equipment.

This crumpling effect by the venturi-nozzle may be used not only during dyeing, but also other steps such as preor after-treatments, and in any case a graceful synthetic suede is obtained.

Aqueous liquid is preferable as the fluid of this invention. This liquid may comprise plain water or it may contain dyestuffs and dyeing assistants such as acids, alkalis and surfactants.

Dyeing equipment which is adaptable to receive and use a venturi-nozzle of this invention is described, for example. in U.S. Pat. No. 3,510,251. The number of passages of the napped sheet through the venturinozzle affects the flexibility of the product. In this invention, the napped sheet is required to pass the venturi-nozzle at least about ten times. Further, the flow rate of fluid upon passing the venturi-nozzle influences the flexibility and the appearance of naps. The preferred flow rate is in the region of about 20l 50 m/min. The preferred temperature of dyeing of this invention is about -150C. preferably about ll0l40C. A sheet dyed at a higher temperature than above tends to develop cracks on its surface; on the other hand, a sheet dyed at a lower temperature than above mentioned tends to experience uneven dyeing because of lowering the dye adsorption of the fibers. Soaping and reduction clearing after dyeing are preferred treatments to improve the color-fastness of the products.

EXAMPLES The invention is further illustrated by the following examples. The measurements offlexibility" appear ance of naps". writing effect, uneven dyeing", resistance to dyeing and color fastness in the examples are described as follows.

Flexibility is defined as the force in grams required to bend, through a deflection of 2 mm, a sample of 2 cm X 5 cm, which sample is restrained at spaced points 1 cm apart at a common level. The bending is accomplished by a pull rod which contacts the sample midway between the spaced points and the pull rod is preferably connected to a load cell to measure the required force. One such apparatus is the Shimazu Autograph 180.000. The sheet which possesses a value below 100 grams is considered especially flexible. The lowering ratio of flexibility value is defined as follows:

wherein A is the flexibility of the sheet before dyeing and B is the flexibility of the sheet after dyeing.

Appearance of naps" is defined as the degree of pilling by ASTM Dl375-67 (random tumble pilling tester). The classification of the appearance of naps by the observation of thirty persons corresponds to the degree of pilling test by said ASTM designation.

Writing effect is judged by the observation of thirty persons. Class 5 indicates that above percent of them consider the writing effect good, Class 4: 70-90 in accordance with EXAMPLE 1 A. Preparation of non-woven fabric A non-woven web was made from islands-in-a-sea type staple fiber of 3.4 denier. 49 mm length. 5 crimps/in. and a draw ratio of 2.3 which comprised 50 parts of island component of polyethyleneterephtalate whose intrinsic viscosity was 0.66 and 50 parts of sea component containing 47 parts of polystyrene and 3 parts of polyethylene glycol. said island component distributing as 16 islands in the sea component when seen as a cross-section of the fiber and it was processed by needle punching to produce a non-woven fabric of a density of (H60 g/cm. Said non-woven fabric was immersed in a 20 percent aqueous solution by weight of polyvinyl alcohol and after drying it was immersed in perchlorethylene to dissolve the sea component (polystyrene). Thus the non-woven fabric of this invention which comprises the superfine denier fiber was obtained. B. Preparation of the block polyurethane 1 mol of diol mixture which comprises parts of polycaprolactone diol of a molecular weight of 1800 and 70 parts of polytetramethyleneetherglycol of a molecular weight of 2000. and 2 mols of diphenylmethane -4.4-diisocyanate was reacted for 2 hours at 80C to by buffing. The napped sheet had a thickness of 0.95 mm and a width of cm. Then each sheet was dyed in the dyeing equipment called circular manufactured by Hisaka Works. Ltd.. which was equipped with a cylindrical venturi-nozzlc having an internal crosssectional area of 20 cm (the ratio of the crosssectional area of the nozzle to that of the sheet was 4.21 and a length of 20 cm. said sheet passing through the venturi-nozzle at the rate of m/min. for 1 hour at 130 C and the dyeing bath containing 2 percent o.w.f. Kayalon Polyester Gray NG (NIPPON KAYAKU).

Properties of each sheet after finishing buffing are shown in Table l. Elongation and strength of the fiber which was obtained from the sheet before dyeing by extracting the polyurethane with dimethylformamide were 92 percent and 0.8 grams respectively. The denier of the fiber was 0.12.

It is clear from Table 1 that though the sheet of this invention was rather stiffer than the comparative sample before dyeing. it became remarkably flexible after dyeing. on the other hand the comparative sample became only slightly flexible. The ratio of reduction of flexibility of the former was 48.2 percent. on the other TABLE I (Example 1 Properties of Sheet Flexibility Ratio of Tensile Properties Judg- (gl reduction properties of nap ment of flexof sheet (class) ihility('/( after dyeing before after strength elongawriting dyeing dyeing (g/cm) tion('/r) appearance effect This Very invention I 88 48.2 78 92 5 5 good Comparison I50 I42 4.7 82 90 2 2 Poor EXAMPLE 2 yield an isocyanato-terminated intermediate called a prepolymer. After dissolving the prepolymer in dimeth- A non-woven fabric of this invention was prepared in ylformamide to give a solution of 50 percent by weight. 50 accordance with Example L Substituting a draw ratio the mixture of 1 mol of 4.4-diaminodiphenylmethane and dimethylformamidc was added slowly to 50 percent solution to give a 15 percent solution.

A 15 percent solution of polyurethane as a comparative solution was prepared by the above-described 55 method using only polytetramethyleneetherglycol instead of the diol mixture.

13 percent dimethylformamide solution of the block polyurethane elastomcr of this invention was prepared using a diol mixture comprising 25 parts of polycaprolacetone of molecular weight 1,500 and parts of polytetramethyleneetherglycol of molecular weight 1.500 in accordance with method (B) in Example 1. Further. l3 percent dimethylformamide solutions of polyurethane. as comparisons. were prepared using only the above polycaprolacetone diol and using a diol mixture comprising 50 parts of the above polycaprolacetone diol and 50 parts of the above polytetramethyleneetherglycol separately.

The non-woven fabric ofthis invention was immersed in each polyurethane solution and the resulting napped and impregnated sheet had a thickness of 0.95 mm and a width of 50 cm in accordance with the method (C hand that of the latter was only 4.7 percent. The tensile in Example 1. Each sheet was dyed in the manner of Example 1 using a cylindrical venturi-nozzle having a cross-sectional area of its hollow part of 35 cm (the ratio of nozzle to sheet is 7.73) and the dyestuff mix ture comprising 8 o.w.f. percent of Kayalon Polyester Light Red BF (Color Index No. Dis. Red 152) and 2 o.w.f. percent Kayalon Polyester Scarlet RSF (Color Index No. Dis. Red 143). The properties of fiber obtained from each sheet before dyeing were as follows: strength: 1.2 grams. elongation at break: 85 percent and denier: 0.09. The properties of each sheet are shown in Table 2.

It is clear that the sheet of this invention showed good appearance of nap and had a flexible touch. on the other hand the comparison 1 using polycaprolacetonepolyurethane had an extremely poor dyeing resistance. Further. the comparison 2 using polyurethane comprising a diol mixture deviating from the extend of this invention showed poor dyeing resistance, though better than comparison 1. such as lowering of strength of the sheet and development of cracks on its surface. poor appearance of nap and poor flexibility (the ratio of flexibility reduction was only 6.4 /1).

TABLE 2 (Example 2) Properties of Sheet a thickness of 0.8 mm and a width of 90 cm were obtained. Each sheet was dyed in the manner of Example 1 using a cylindrical venturi-nozzle having a crosssectional area of its hollow parts of 60 cm (the ratio of nozzle to sheet is 8.33). The properties of fiber were as follows: strength: 0.700.90 grams. elongation at break: 91-93 percent and denier: 0.12.

Among the examples of this invention No. 3-2 using an aliphatic diamine was slightly inferior to No. 3-] using an aromatic diamine with respect to properties of nap and dyeing resistance. Also No. 3-3 using aliphatic diisocyanatc was inferior to No. 3-1 and to No. 3-4 using aromatic diisocyanate with respect to such properties. Among the examples using aromatic diisocyanate. No. 3-1 using dipheny1methane-4,4-diisocyanate was better than No. 3-4 using tolylene diisocyanate with respect to flexibility and properties of nap. Among the samples using various ratios of polycaprolactone to polytetramethylenneetherglycol in the diol mixture. No. 3-1 using a ratio of /70 and No. 3-6 using 20/80 showed good properties in all respects. but No. 3-5 using 40/60 was slightly inferior with respectto the properties of nap and dyeing resistance. Though these Flexibility Ratio Tensile Properties Resist- Judg- (g) of flu properties of of nap ance to men! ihility sheet after (class) dyeing reduction dyeing before after (/1 strength elongaappear- \\'rit dyeing dyeing (g/em'') tionU/r ance ing effect This 172 85 81 88 5 5 very good very invention good Comparison 210 320 0 3| 42 l 1 large and deep cracks. Poor tear and wear Comparison 185 173 (1.4 62 2 2 numerous Poor 2 small cracks examples of this invention had some defects. they EXAMPLE 3 Various 15 percent dimethylformamide solutions of polyurethane shown in Table 3 were prepared in accordance with the method (B) in Example 1. The nonwoven fabric obtained in Example 1 is immersed in those solutions and the resulting napped sheets having showed an effective flexibility value of above 20 percent. On the other hand. the comparison 1 using a diol ratio of 10/90 showed little flexibility value reduction (only 6'72) and comparison 2 and comparison 3 using a polyurethane whose structure deviated from this invention provided unsatisfactory sheets.

TABLE 3 Example 3 Polyurethane Properties of Sheet Polyester Polyether Diiso- Chain Flexibility Reduc- Tensile Resis- Properties of Judg- Parts Parts eyanate Ex (g) tion properties of tance nap ment (MW) (MW) tender ratio of dyed sheet to (class) before after flexstrength elongadyeing Appear- Writing dyeing dyeing ibility g/cm") tion( "/1 anee effect The PClJ'" PI'MG MDl MBA 169 79 53.2 84 very invention 1.980) (2.020) good 5 5 very 3- good The PCIJ' PTMG MDl TMD 162 94 42.0 72 95 good. 4 4 good invention 1.980) (2.020) but slight cracks occur The PClJ'" PIMG HMDl MBA 1610 108 32.5 71 80 good. 3 3 good invention 1.980) (2.020) but 3-3 slight cracks UCClll' TABLE 3 Continued (Example 3) Polyurethane Properties of Sheet Polyester Polyether Diiso- Chain Flexibility Reduc- Tensile Resis- Properties of Judg- Parts Parts cyanate lix- (g) tion properties of tance nap ment MW) (MW) tender ratio of dyed sheet to (class) before after flexstrength elongadyeing Appear- Writing dyeing dyeing ihility (g/cn1'-) tion( /1 ancc effect The PCU" PTMG" TDl MBA b )8 38.0 75 )1 good 4 3 good invention 1.980) (1020) 3-4 The P(l. PTMG' MDl MBA 1'78 105 41.0 74 82 good. 4 3 good invention 1.980) (2.020) but 3-5 slight cracks occur The lClf'" PTMG" MDl MBA 157 82 47.14 87 8*) very 5 5 very invention 1.980) (2.020 good good 3-0 (ompari- PCL'" PTMCI MDl MBA 151 142 6.0 85 88 very 2 2 poor son I 1.980) (2.020) good (ontpari- PClf PPG MD] MBA 195 192 1.5 65 72 good. 2 2 poor son I 1.750) (2.050) but slight cracks occur Compari- PEA PTMG MDl MBA 205 220 0 45 4X tear 1 1 poor son 3 (3.030) 1.870) and wear cracks PCL: polycnprolactone diol Pl-.A: polycthylcncadipatc P'I'MG: i\lytetramethylenecthcrgly col PP(i; polypropy lcncclhcrglycol MDl: diphenylmcthtmc-4A'-diisocyanatc TD]: 2.4-to1ylcncdiisocyanatc HMDl: hcxunicthylencdiisocyanalc MBA: 4.4-dianiinodipheneylniclhanc TMD: trimcthy lcncdiaminc EXAMPLE 4 1 using a dyestuff mixture of 1 percent of Tcrasil Orange 5RL and 5 percent of T.D. Brill Scarlet D-FGL. A non-woven fabric of this invention was prepared in The properties of each product are shown in Table 4. accordance with Example 1 substituting a draw ratio of lt is clear from Table 4 that the sheet of this invention 2.2 and a comparison sample was also prepared substiis flexible and the ratio of flexibility reduction was 49 tuting a draw ratio of 4.0. percent. Further. the dyeing properties of this sheet Each non-woven fabric was immersed in the 13 perwas very good and without unevenness, on the other cent dimethylformamide solution of the block polyurehand the comparison sample using a polyethane obtained by reacting a diol mixtue of 30 parts of thyleneterephtalate of low elongation at break showed polycaprolactone diol of a molecular weight of 1,200 poor flexibility and further remarkably uneven dyeing and 70 parts of polytetramethyleneethcrglycol with dibetween naps and skin, i.e. the naps were dyed red and phenylmethane-4,4-diisocyanate and 4,4'- the polyurethane was dyed yellow. Both sheets had aldiaminodiphenylmethane. The resulting napped sheet most the same value of tensile strength and good colorhad a thickness of 0.95 mm and a width of cm and fastness which was far superior as compared with natuwas dyed in accordance with method (C) in Example ral suede.

TABLE 4 (Example 4) Properties of PET fiber Properties of dyed sheet Denier Breaking Breaking Flexibility Properties of naps Dyeing properties Tensile properties Judgment strength elongation (g) (class) (g) (7:) appearwriting uneven color strength elongation ance effect dyeing fastness (g/cm*) 7!) (class) This 0.1 l 0.78 101 81 5 5 good dry 4 82 88 Verv invention. wet 3-4 good Compari- 0.12 3.5 33 250 l 2 poor dry 4-5 85 82 Poor son color wet 3-4 difi'er- BHCC bc- [\Vfitfn naps and skin Natural 5 5 good dry 2 92 45 Good suede we! 1-2 PE l: polyethy lcltcturephthalate 15 EXAMPLE A non-woven fabric was made from islands-in-a-sea type staple fiber of 3.4 denier. 49 mm length. crim'p s/in and a draw ratio of 2.3 which comprised parts each sheet are shown in Table (i. No. 6-1 is an example of the sheet dyed with Jigger type dyeing equipment, and it was not desirable because of causing a decrease of thickness by tension during dyeing and the anisotof island component of polyethyleneterephtalate whose 5 ropy of elongation, though the appearance of the naps intrinsic viscosity was 0.66 and 50 parts of sea compo was good. No. 6-2 was an example ofa dyed sheet using nent containing 45 parts of polystyrene and 5 parts of a Tumbler type dyeing equipment which crushes a polyethyleneglycol in accordance with method (A) in sheet only with the flow of dyeing liquid. and it showed Example 1. A Comparison sample was also prepared i insufficient flexibility (the flexibility value reduction the same manner. only substituting a draw ratio of 1.8. 10 a only -5 and P 1111p P P On the Othfir Both non-woven fabrics were converted to napped hand. the example of this invention showed no anisotand dyed sheets in accordance with Example 4. The ropy and showed sufficient flexibility and preferred nap properties of both sheets are shown in Table 5. properties.

TABLE 6 (Example 6) Properties of Sheet dyeing flexibility Ratio of Thickness of Breaking elongation of sheet Properties of Judgequipment (g) flexsheet longitudinal transverse nap ment ibility (mm) 71 (class) before after reducbefore after before after before after appearance writing dyeing dyeing tion dyeing dyeing dyedycdycdyeeffect ing ing ing ing This Example I 88 46.7 ".0 Z. 88 88 5 5 very invenl good tion (ompari- Jigger 165 I85 0 2.0 1.1 88 48 88 M0 5 5 poor son 6-l Compari Tumbler 165 156 5.5 2.0 2.0 88 87 8X 88 2 2 poor son (F2 EXAMPLE 7 The dyed sheet of this invention had a practical strength and good recovery characteristics. On the other hand. the comparison sample using the high elon- The napped sheet before dyeing obtained in accordance with Example I was dyed using the various cylingatkm fibers had P Strength for Practical use and 35 drical venturi-nozzles shown in Table 7. The dyeing poor recovery characteristics which tended to cause trouble upon wearing. such as the trousers bagging at the knees. for example.

TABLE 5 method was in accordance with (C) in Example 1. The properties of the resulting dyed sheets are shown in Table 7. The dyed sheet of this invention was flexible (Example 5) Properties of PET Properties of dyed sheet fibers Tensile properties Tensile Judgment denier breaking breakstrength elongation recovery (71) strength ing (g/cm (/2 (3071 elongag) elongation) tiont after after 1 hr. 10 his.

This 0. l0 0.8] 85 87 80 92 Very Invention good Compari- 0.1 l 032 220 56 l30 41 60 Poor son EXAMPLE 6 and had good nap properties and dyeing resistance. On

the other hand. the comparison sample I using the ex- 55 cessively small venturi-nozzle showed tear and wear during dyeing and the comparison sample 2 using the excessively large venturi-nozzle showed no effect of flexing and poor appearance of naps.

TABLE 7 Cross sectional (Example 7) Properties of Sheet area of hollow Flexibility Ratio of Tensile properties Properties of nap Resistance Judginternal throat (g) flexibility of dyed sheet (class) to dyeing ment of venturibefore after reduction strength elongation appearance writing nozzle (cnf) dyeing dyeing ("/1 (g/cn'F) (7:) effect This 20 I72 85 50 81 88 5 5 good very invention (42] d Compari- 5 l72 81 52.9 56 l l tear and wear poor son I L05) cracks loosing TABLE 7 Continued (Example 7) Cross sectional Properties of Sheet area of hollow Flexibility Ratio of Tensile properties Properties of nap Resistance Judginternnl throat (g) flexibility o1" dyed sheet (class) to dyeing ment of venturibefore after reduction strength elongation appearance writing nozzle (cm dyeing dyeing ('s) (g/cm") /r) effect Compari- 130 172 155 9.9 81 80 2 2 good poor son 2 (28.4)

i shows the ratio of the cross-sectional area of the throat of \cntnri-no/7le to that ofthe sheet.

EXAMPLE 8 The napped sheet before dyeing obtained in accordance with Example 1 was dyed at various temperatures shown in Table 8. The dyeing method was in accordance with (C) in Example 1. The properties of the resulting sheets are shown in Table 8.

The comparison 1 dyed at 60C was an insufficiently colored product whose fiber component did not dye at all. the comparison sampleZ dyed at 160C showed numerous cracks on its surface and exhibited tear and wear in many places. On the other hand, the invention samples 1 and 2 showed a softening effect through dyeing and good nap appearance. Among these inventions. No. 2 dyed at 100C required a long dyeing time and showed an insufficiency with respect to depth of color tone. and slightly deficient flexibility as compared with No. 2 dyed at 125C.

and

TABLE 8 Example 8 Properties of Sheet Temperature Flexibility Ratio of Tensile properties Properties of nap Resistance Judgment of (g) flexibility of dyed sheet (class) to dyeing before after reduction strength elongation appearance writing dyeing (C) dyeing dyeing (/1 g/cm") ("/1 effect Comparison 172 168 2.3 92 2 2 good. but poor 1 10 hrs.) insufiicicnt color This 172 108 37.2 X5 90 4 3 good. but good invention (5 hrs.) insufficient 1 tone of color decpness This 172 87 49.4 83 91 5 5 good very invention 1 hr.) good '7 Comparison 172 75 56.4 41 120 1 1 tear and poor 2 1 hr.) wear cracks shows the time of dyeing.

EXAMPLE 9 wherein S is the reduced cross-sectional area and A is A polymer blend type superfine denier fiber was prepared from 30 parts of polyethyleneterephtalate in the manner of Example 1 and 70 parts of polystyrene. A nonwoven fabric was prepared in accordance with Example 1 using said polymer blend type fiber. A napped sheet was prepared in accordance with Example 1 and the properties of the fibers of the sheet were as follows: denier: 0.07. strength: 1.5 grams, elongation: 85 percent. The napped sheet was dyed in accordance with Example 1. The resulting product shows preferred flex ibility. though it was inferior to the product made of islands-in-a-sea type fibers in respect of density of nap and writing effect. The properties were as follows:

flexibility (g) before dyeing: 160 after dyeing: 108 Flexibility reduction ratio (7r): 32.5 Properties of nap (class) appearance: 4 writing effect: 3

the cross-sectional area of the napped sheet (cm' said napped sheet having naps of superfine denier fiber on at least one surface thereof and having a thickness of about 0.2-4.0 mm and a width of about 5-200 cm. and comprising (a) nonwoven fabric made up of 0.1-0.3 denier superfine staple fibers having .a breaking strength of below 3 grams and an elongation at break of 60-180 percent. said fibers being adhered to (b) a polyurethane elastomer comprising the reaction product of a diol mixture consisting essentially by weight of 20-40 parts of polycaprolactone diol having a molecular weight of about 1000- 3000 and 60-80 parts of polytetramethyleneetherglycol having a molecular weight of about 1000-3000 with an organic diisocyanate and a diamine chain extender and repeatedly contacting the suede with the dye liquid after the suede emerges from the said area of reduced cross-section.

2. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the flow rate of the fluid in said reduced area is in the range of about 20-150 m/min.

3. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the napped sheet is passed with a fluid through a venturi opening at a temperature of about 80-l50 C.

4. A process for crumpling synthetic suede leather sheet material as claimed in claim I wherein the napped sheet is passed through said reduced area repeatedly at least about 10 times.

5. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the ratio of polyurethane elastomer weight to the nonwoven fabric weight in the napped sheet is in the range of about 20/l00l0O/l00.

6. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the denier of the superfine fiber is 0.050.2.

7. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the superfine denier fiber is a polycthyleneterephthalate.

8. A process for crumpling synthetic suede leather sheet material as claimed in claim 7 wherein the napped sheet passes with a fluid through a venturi opening at a temperature of 100l40 C.

9. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein a superfine denier fiber is such fiber that is obtained by dissolving at least one component from a multicomponent fiber with a solvent. said multi-componcnt fiber comprising at least two different polymers.

10. A process for crumpling synthetic suede leather sheet material as claimed in claim 9 wherein the multicomponent fiber is an islands-in-a-sea type fiber which forms a fiber bundle when the soluble component is dissolved said fiber bundle being formed by fine filaments which are continuous along the fiber axis.

11. A process for crumpling synthetic suede leather sheet material as claimed in claim 9 wherein the multicomponcnt fiber is a filament of an intimate mixture of two mutually incompatible fiber-forming organic polymers.

12. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the diol mixture comprises about 20-35 parts of polycaprolactone diol having a molecular weight of about 1000 3000 and about 65-80 parts of polytetramethylenee- 2O therglycol having a molecular weight of about l0003000.

13. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the organic diisocyanate is an aromatic diisocyanate.

14. A process for crumpling synthetic suede leather sheet material as claimed in claim 13 wherein the aromatic diisocyanate is diphenylmethane-4 4'- diisocyanate.

15. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the diamine chain extender is an aromatic diamine.

16. A process for crumpling synthetic suede leather sheet material as claimed in claim 15 wherein the aromatic diamine is 4.4-diaminodiphenylmethane.

17. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the organic diisocyanate is diphenyl methane-4,4- diisocyanate and the diamine chain extender is 4,4- diaminodiphenylmethane, and the structure of the polyurethane el astomer is shown in the formula'as follows:

H ll I C-N p is an integer of l3 and n is an integer of at least l. 18. The method defined in claim 1 wherein said-area of reduced cross-section is circular in shape.

UEITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3, 899, 292

DATED 8/12/75 MS) Kaoru Okazaki; Kenkichi Yagi; Miyoshi Okamoto; Koji Watanabe;

It is certified ?I?a t %pr o r gpp%a 1r ?r ThB a I JE V EEEKIIe rP %atr% m that said Letters Patent is hereby corrected as shown below:

Column 18, line 20, delete 2 s/A 22" and insert --2 S/A 22--.

Column 18, line 25, delete 10 S 300 (cm and insert ---10 S 300 (cm Signed and Sealed this Twenty-third Day of October, 1990 Arrest:

HARRY F. MANBECK. JR.

Arresting Ofiicer Commissioner of Patents and Trademarks 

1. A PROCESS FOR PREPARING SYNTHETIC SUEDE, SAID SUEDE COMPRISING A NAPPED NEEDLE-PUNCHED FIBRIC COMPRISING A MULTIPLICITY OF FIBERS OF SUPERFINE DENIER INTO WHICH POLYURETHANE IS IMPREGNATED, SAID PROCESS COMPRISING REPEATEDLY CRUMPLING SAID NAPPED SHEET BY PASSING IT TOGETHER WITH A DYE LIQUID THROUGH AN AREA OF REDUCED CROSS-SECTION ACCORDING TO THE RELATIONSHIPS:
 2. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the flow rate of the fluid in said reduced area is in the range of about 20- 150 m/min.
 3. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the napped sheet is passed with a fluid through a venturi opening at a temperature of about 80- 150* C.
 4. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the napped sheet is passed through said reduced area repeatedly at least about 10 times.
 5. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the ratio of polyurethane elastomer Weight to the nonwoven fabric weight in the napped sheet is in the range of about 20/100- 100/100.
 6. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the denier of the superfine fiber is 0.05- 0.2.
 7. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the superfine denier fiber is a polyethyleneterephthalate.
 8. A process for crumpling synthetic suede leather sheet material as claimed in claim 7 wherein the napped sheet passes with a fluid through a venturi opening at a temperature of 100* -140* C.
 9. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein a superfine denier fiber is such fiber that is obtained by dissolving at least one component from a multi-component fiber with a solvent, said multi-component fiber comprising at least two different polymers.
 10. A process for crumpling synthetic suede leather sheet material as claimed in claim 9 wherein the multi-component fiber is an islands-in-a-sea type fiber which forms a fiber bundle when the soluble component is dissolved, said fiber bundle being formed by fine filaments which are continuous along the fiber axis.
 11. A process for crumpling synthetic suede leather sheet material as claimed in claim 9 wherein the multi-component fiber is a filament of an intimate mixture of two mutually incompatible fiber-forming organic polymers.
 12. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the diol mixture comprises about 20- 35 parts of polycaprolactone diol having a molecular weight of about 1000 - 3000 and about 65- 80 parts of polytetramethyleneetherglycol having a molecular weight of about 1000-
 3000. 13. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the organic diisocyanate is an aromatic diisocyanate.
 14. A process for crumpling synthetic suede leather sheet material as claimed in claim 13 wherein the aromatic diisocyanate is diphenylmethane-4,4''-diisocyanate.
 15. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the diamine chain extender is an aromatic diamine.
 16. A process for crumpling synthetic suede leather sheet material as claimed in claim 15 wherein the aromatic diamine is 4,4''-diaminodiphenylmethane.
 17. A process for crumpling synthetic suede leather sheet material as claimed in claim 1 wherein the organic diisocyanate is diphenyl methane-4,4''-diisocyanate and the diamine chain extender is 4,4''-diaminodiphenylmethane, and the structure of the polyurethane elastomer is shown in the formula as follows:
 18. The method defined in claim 1 wherein said area of reduced cross-section is circular in shape. 